Antibiotic production,among the several characteristics of temporally regulated gene expression in Streptomyces, is the major reason for the considerable fundamental and applied scientific interest in these filamentous soil bacteria. Acquisition of new knowledge about the genetic and biochemical basis of antibiotic production will lead to ways to make new antibiotics and to improve their commercial production. It also will provide significant information about prokaryotic molecular biology. Polyether antibiotics, currently used as coccidiostats and bovine growth promotants, are the subject of this proposal for continuing our research on the biosynthesis. The long-range goals are to learn how the microorganisms can make polyethers in such characteristically large amounts by investigating the regulation of antibiotic production, and to learn how they assemble the intricate carbon skeleton of polyether antibiotics by studying the properties of polyether polyketide synthases and the corresponding genes. During this grant period, we will characterize the monensin polyketide synthase and resistance genes by complementation experiments, DNA sequencing, and transcriptional analysis. We will compare the structures of the monensin and salinomycin polyketide synthase genes and predicted gene products. The metabolites accumulated by Mon mutants will be characterized by chemical and spectroscopic analyses to help us identify the properties of monensin production genes. We will clone the valine dehydrogenase genes from S. coelicolor and S. cinnamonensis to study the regulation of vdh expression and the possible connection of valine catabolism to monensin production. finally, we will investigate the genetic basis for the frequent loss and restoration of lasalocid production of S. lasaliensis by following the behavior of the lasalocid polyketide synthase gene in protoplast fusion.